Fluorite from Mihalkovo in the Rhodope mountains / Bulgaria
by Robert Kunze
Fluorite is a common and well known mineral with many fans all over the planet. Specimens with fantastic quality belong to the most wanted items in the mineral world. We know dozens of locations that famous for excellent fluorite-specimens, e.g. Freiberg, Illinois, Yaogangxian, Dalnegorsk, Riemvasmaak, Weardale or the Alps.
But not only high quality-specimens or aesthetic items are on the wish-list of fluorite-collectors. Many of them are also interested in specimens from less known locations or single finds from a location. Other localities produced only a few specimens with crystals. Examples for locations that are less known are Blegos mountain in Slovenia, Moldova in Czech Republic or Mihalkovo in Bulgaria.
A few months ago I had no idea about fluorite from Bulgaria. The country in southeast Europe is not known for that. In an older collection I found 2 pieces that caught my attention. Green cubes, only 1 cm large with a naturally etched surface on matrix. Nothing spectacular, but for me worth doing more research about it.
Bulgaria is located in southeast Europe between Romania in the north and Greece in the south. The country with approx. 7,2 mio. people has a long history of mining. The most known location is Madan.
Due to it's size and number of mines in this country fluorite, is quite rare. There are only a hand full of deposits and not all of them are big enough for commercial mining. One of the locations fluorite was produced is Mihalkovo. Mihalkovo is the name of a small village in the south of Bulgaria (Oblast Smoljan). It is situated in the Rhodope mountains, approximately 35 km north of the border to Greece and 40 km southwest of Plowdiw.
figure 1: The village of Mihalkovo marked in the center of the map with the greek border in the south and the city of Plowdiw in the northeast (image taken from google earth)
The mine itself is located 2,5 km north of the village at 600 m above sea-level near an artificial lake. Because of its relatively small size, compared to other huge deposits, there are only few information available.
figure 2: a detailed aereal view on Mihalkovo area with the river Vacha running from south to north (image taken from google earth)
figure 3: close up on the mining area east of the river Vacha (image taken from google earth)
figure 4: close up on the mining area from another direction (image taken from google earth)
The mine was productive until 1994. The fluorite was mined to produce a concentrate of hydrofluoric acid which is used in chemical industries. Unfortunately I could not find any additional information about the production-period.
figure 5: the only photo I found from the mine of Mihalkovo (image taken from google streetview)
The following information were taken from BOGDANOV, B.; 1982; Mineral deposits of Bulgaria; in: Min. desposits of Europe, Vol.2, South East Europe, The Min. Soc.; Instit. of Mining and Metallurgy.
„The area of the deposit is composed of Proterozoic (?) metamorphic rocks represented by alternating chlorite-schists, gneis, amphibolites and marbles. The marble beds at the contacts with schists, amphibolites and gneises, are replaced by fluorite.
Thus irregular layered deposits and nests were formed ranging in thickness from 1 to 12 m; up to 300 m in Iength and 20 - 30 m in width which tend to occur mainly at the upper contacts of the marbles with the metamorphic schists. They comprise fluorite, quartz and barite with impregnations of galena, sphalerite, pyrite and clay-minerals. The fluorite content varies from 10 to 70%.
It forms massive aggregates or druses of cubic and cubic-octahedral crystals up to 1-2 cm in diameter. It is green, colourless or violet. The deposit was formed in several stages during which the quartz-sulphide and the quartz-fluorite paragenesis with calcite and barite was successively formed. The deposit is of hydrothermal-metasomatic type and was emplaced at shallow depth at temperatures ranging from 60°C to 250°C. The principal part of the fluorite was deposited at a temperature of 115-225°C. [...]"
The mine is closed since 1994 and I was told that there is no access possible. No new finds can be expected. If you take a look at the fluorite, you will see that this kind is unique. The combination of the crystals habit and the matrix are typical for this Mihalkovo. The matrix consists of porous gneiss with a light yellow color. The stone seems to be fragile, not very stable. Some parts can be removed by hand! But it doesn't mean that the specimens are unstable...
figure 6: at this photo you can see the typical matrix of the specimens in combination with some deep violet fluorite, size: 14,5 cm
The fluorite is situated on the gneiss and very well crystallized in druses. The fluorite is crystallized as octahedrons manly, I would say about 95% of the specimens show this habit. A few items were found with cubic crystals. Both kinds have something in common, very typical for Mihalkovo: the crystals surface is very fine stepped; the faces are not sharp terminated. The color ranges from light to middle green over colorless to violet.
figure 7: truely one of the best specimens with typical green crystals in association with some white quartz, size: 10,5 cm
figure 8: close up of the previous specimen to show the color and the crystal-habit with the interesting structured faces, FOV: 4 cm
As far as I know green is the common color for fluorite of this location. Violet fluorite was quite rare and I have only seen one specimen with colorless crystals so far. Some items show green crystals with a violet center, very appealing!
figure 9: one of the few specimens that show a second gerneration of pale white fluorite on top, size: 9 cm
figure 10: close up of the previous specimen with both fluorite-generations, FOV: 3,5 cm
figure 11: a fantastic specimen that shows crystals with a violet center under the green outer layer in very good condition, size: 10,5 cm
figure 12: another fine specimen with bicolored fluorite from Mihalkovo, size: 6,5 cm
In the article above are some other minerals mentioned from Mihalkovo. Personally I have not seen another mineral from this location. At a few specimens I found some tiny quartz-crystals. But it's really not worth talking about.
Well, after a longer search I could buy about 30 specimens from an older collection. The specimens were found by a former miner in Mihalkovo. These 30 specimens were everything he had collected in this mine, so I was very happy to get them. As the specimens arrived I thought about a new find. The items looked very fresh, uncleaned. I found a lot of dirt on the crystals, sometimes also small roots! So I had to clean first of all.
Now, please enjoy some more photos of specimens from this unknown location.
figure 13: one of the few specimens I saw with cubic fluorite-crystals, size: 9 cm
figure 14: close up of the prevous specimen, FOV: 3 cm
figure 15: one of the best structured specimens so far, size: 10,5 cm
figure 16: close up of the previous specimen to show the typical surface and luster, FOV: 3,5 cm
figure 17: in my mind one of the best items from this find, size: 9,5 cm
figure 18: on this specimen you can see the rest of a white mineral between the fluorite. It is not hard and can be removed with a steel needle. Size: 9 cm